(Received 5 November 1996; accepted 25 November 1997) ... Bending strength and stiffness of Norway spruce (Picea abies) from three stands in ... more significant for the studs from the slow-grown stand than from the fast-grown ones. .... industry and

ABSTRACT: Biochar (BC), the carbon-rich by-product resulting from pyrolysis of biomass, is used for bioenergy and increasingly as a soil additive for carbon sequestration and soil improvement. However, information about the effects of BC on forest productivity and reforestation success, especially on boreal and temperate forest soils, is scant. We examined the effects of two BC types (Canadian and Finnish) added in proportions up to 60 vol.% into a common alluvial silty soil on the growth of transplanted Norway spruce (Picea abies [L.] Karst.) seedlings in a growth chamber. We found no marked differences in seedling growth among the binary growing media mixes used. Seedling growth attributes (seedling height, terminal shoot growth, root volume) differed consistently only between the BC types in the highest proportion used. The terminal shoot growth differed overall among the two BC types. These results suggest that BC may be applied into mineral soils without detrimental chemical effects on tree plantation success. Our results provide foundation for further field research on the longer-term impacts of adding BCs to boreal forest soils. Keywords: carbon sequestration; forest soils; soil additives; outplanting success; pyrolysis

al. 2008; Blackwell et al. 2009; Brockhoff et al. 2010; Mcelligott et al. 2011). Recent results from US temperate forests suggest that pyrolyzed BC can be returned to forest sites to increase soil nutrient and carbon stocks with little effect on short-term tree growth (Mcelligot 2011). However, practically no information is available about boreal forests; some work with wood ash as a nitrogen-free fertilizer to counteract the loss of nutrients resulting from tree harvesting and soil acidification has been reported (Saarsalmi et al. 2004; Augusto et al. 2008). Fire-produced charcoal usually has no harmful effect on boreal forest productivity although it can affect the growth of tree seedlings and other vegetation (Wardle et al. 1998). Therefore, our objective was to examine effects of two BC types, a Canadian powder from agri125

culture and forestry residues and a coarser Finnish BC from softwood chips, added to a common alluvial silty soil in proportions up to 60 vol.% on the growth of transplanted Norway spruce (Picea abies [L.] Karst.) seedlings in a growth chamber.

Corporation, Richmond, Canada) originating from agricultural or forestry biomass (CBC), which were mixed into alluvial silty soil in volume proportions 0, 15, 30, 45 and 60%. Silty soil was used because of its homogeneity. Ten pots were filled with each medium, resulting in a total of 100 transplanted seedlings (2 BC types × 5 media × 10 replicates). Total (from closed wet HNO3-HCl extract) and soluble exchangeable [cations and P from acid ammonium acetate (pH 4.65) extract and N from KClextract] concentrations of macronutrients (N, P, K, Ca) and boron (B) as well as physical soil properties (bulk and particle densities, total and air-filled porosities, water retention) were measured for the growing media or their components using standard analyses described in Dumroese et al. (2011) (Tables 1 and 2). Media components were measured for particle-size distribution by dry sieving (Fig. 1). The CBC was the same as that described by Dumroese et al. (2011). FBC was of coarser texture than CBC (for more FBC details Tammeorg et al. 2012). pH from 1:5 soil:water suspension was 6.2, 6.8 and 7.7 for CBC, FBC and silt, respectively. Transplanted seedlings were grown in a growth chamber (Type 10’ Sp/5 DU-Pi, Weiss Klimatechnik GmbH, Reiskirchen-Lindenstruth, Germany). Diurnal light cycle was set to no light 4 h, dim 1 h, full light 18 h, and dim 1 h. Full light yielded photosynthetically active radiation at the seedling shoot

MATERIALS AND METHODS Seedlings of a local seed source were grown operationally in a forest nursery in Suonenjoki, Finland (62°64'N, 27°05'E), stored at –3°C from autumn until January, and thawed at 6°C for three days following standard procedures (Heiskanen 2013). After thawing, roots were washed clean with tap water. Root volume was determined using water displacement (Harrington et al. 1994). Mean seedling height and root volume were 19.6 cm and 1.54 cm3 (SD 0.35 and 0.33). Seedlings were transplanted into separate 0.5 l plastic pots (Teku, MQC 9 × 9 × 9.5 cm, Pöppelmann GmbH & Co. KG, Lohne, Germany), which were filled with growing media by hand. The growing media were based on a commercially produced Finnish wood BC (Preseco Oy, Espoo, Finland) originating from partially debarked Norway spruce and Scots pine (Pinus sylvestris L.) chips (FBC, pre-sieved to < 2 mm in particle size) or a commercially produced Canadian BC powder (Dynamotive Energy Systems

(day) and 12°C (night). Relative humidity varied between 30 and 60%, and was about 10 percentage points higher with no light. The target volumetric water content was aimed to equal half the total porosity, a level considered to yield sufficient water and oxygen availability (Wall, Heiskanen 2003). Pots were watered manually 2–3 times per week using tap water to their target gravimetric masses. The resulting mean water content was relatively uniform (39–42% of total porosity) in each growing medium during the growing experiment (Fig. 2) and subsequently air-filled porosity was sufficient (Wall, Heiskanen 2003; Heiskanen 2013). Electrical conductivity was measured from additional seedling pots (3 per growing media mix) using a 5TE sensor and ProCheck hand meter (Decagon Devices Inc., Pullman, USA). Electrical conductivity FBC FBC CBC CBC

Fig. 3. Average electrical conductivity in the different growing media during the experiment (mean ± SD)

was relatively low (< 0.11) in all the media as a consequence of non-fertilization (Fig. 3). Seedling heights were measured weekly. Pot positions were changed twice a week to reduce variation in growing conditions. After 9 weeks, seedlings were harvested and measured for morphological attributes, including root volume as described above. In the seedling growing experiment, the effect of the growing medium on the attributes of seedlings and growing media was tested using two-way (factors = BC type, n = 2 and volume proportion, n = 5) and one-way (factor = mix, n = 10) analysis of variance (SPSS software, SPSS Inc, Chicago, USA). The significance of differences between means was tested using Tukey’s test with one-way ANOVA and the LSD test with two-way ANOVA. (b)(b) 50 50 40 40